I have an Edge 800 and a Fenix 3, occasionally use the navigation features on both.

I put the Open Street Maps on my 800, and have been having good luck with them for the most part. Have you seen this post by DCR on how to do it?

I don't usually pre-plan a route, although I'm doing it more often lately. Normally when I want the Edge to navigate for me I'll touch my destination on the map and have it create a route on the fly. It's set to avoid main highways when possible. This works pretty well for me. When my plans change, I'll just ride around the obstacle or whatever it is that forced the change, watching the map until I find my way back to the route.